1. Field of the Invention
The present invention relates to a method of manufacturing a liquid crystal display panel, and particularly to a method of manufacturing a liquid crystal display panel in which liquid crystal is sealed using a dispenser method.
2. Description of the Prior Art
As a display device of an Audio-Visual (AV) machines and an Office Automation (OA) machines, a liquid crystal display (LCD) panel has been widely used because of its merits including a thin thickness, a light weight, a low power consumption and the like. In the LCD panel, liquid crystal is injected into a pair of substrates opposite to each other. In the LCD panel, an alignment direction of liquid crystal molecules is controlled by an electric field generated by an electrode provided in the substrate, and light irradiated onto the LCD panel is modulated, whereby an image is displayed. For such an LCD panel, recently, demands for a high definition, a larger screen and the like have become stronger. Then, in order to improve a display quality, it is important to inject the liquid crystal between the substrates opposite to each other while keeping a uniformity of a gap between the substrates.
As an injection method of the liquid crystal, there is the following method. Specifically, opposite substrates are adhered to each other except for an area thereof serving as a liquid crystal injection hole by use of a sealing material. Thereafter, the adhered substrates are put in a vacuum container and the vacuum container is brought into in a reduced-pressure state. The pressure in the vacuum container is restored to atmospheric pressure in a state where the liquid crystal injection hole is dipped in the liquid crystal, and thus the liquid crystal is injected by use of differential pressure. There is also a method in which opposite substrates are adhered to each other except for an area thereof serving as a liquid crystal injection hole and an air exhaustion port by a sealing material, the liquid crystal injection hole is dipped in the liquid crystal, and the liquid crystal is sucked therein by exhausting air from the air exhaustion port. Furthermore, there is the following method (hereinafter referred to as a dispenser method). Specifically, under a reduced-pressure atmosphere in a vacuum container or the like, a sealing material is coated onto one substrate, liquid crystal is dropped thereonto, and the other substrate is adhered to the one substrate. Thereafter, the pressure in the vacuum container is restored to atmospheric pressure, and thus the sealing material is hardened (For example, refer to Japanese Patent Laid-Open Hei No. 11 (1999)-326922).
In the method in which the liquid crystal is injected by use of the differential pressure or the air exhaustion, the liquid crystal injection port need to be sealed by resin or the like after the liquid crystal injection. A problem that air bubbles are mixed into the liquid crystal from this sealed portion occurs, a problem that the liquid crystal is contaminated with the sealing material occurs, and other problems occur. The dispenser method can shorten an injection time of the liquid crystal drastically compared to other methods. Furthermore, since a required amount of expensive liquid crystal can be reduced, the dispenser method is one that can reduce a cost of an LCD panel. Particularly, the dispenser method is one that is expected in a large-sized LCD panel.
In the above described dispenser method, generally, liquid crystal is injected by use of a first seal (also called a main seal) formed so as to surround a display area and a second seal (also called an auxiliary seal) formed outside the first seal. Furthermore, this dispenser method is roughly classified into two. One is a method in which the second seal is formed to a shape that is a closed curved, and the other is a method in which the second seal is formed to a shape that is an open curved.
Among the two methods, the dispenser method in which the second seal is formed to the shape that is the closed curved will be described with reference to FIG. 1 and FIG. 2. FIG. 1 is a plan view showing a state where liquid crystal is dropped in the method of manufacturing an LCD panel using the conventional dispenser method, and FIG. 2 is a sectional view taken along the line II-II of FIG. 1, which shows a state where substrates opposite to each other are adhered.
First, a sealing material made of ultraviolet cured resin or the like is coated onto one of the pair of substrates opposite to each other (herein a first substrate 2) by use of a screen printing method, a dispenser rendering method or the like. The first substrate 2 has a surface that has been subjected to an alignment treatment. Subsequently, a first seal 4 for defining an area where a liquid crystal material 6 is sealed is formed so as to surround a display area, and a second seal 5 for forming a reduced-pressure area is formed outside the first seal 4 so as to surround the first seal 4.
Next, under a reduced-pressure atmosphere, a proper amount of the liquid crystal material 6 is dropped onto the display area surrounded by the first seal 4 by use of a dispenser for dropping liquid crystal, or the like (see FIG. 1). Subsequently, the other substrate (herein a second substrate 3) in which spacers 7 such as polymer beads and silica beads are scattered is allowed to match the first substrate 2. Thereafter, the vacuum container is restored to an atmospheric pressure state, and both substrates are pushed to each other as shown by the arrows of FIG. 2 by use of the differential pressure between reduced pressure and atmospheric pressure. Thus, the first and second seals 4 and 5 are squeezed, and a desired gap is formed. Then, the first and second seals 4 and 5 are completely hardened, and the liquid material 6 is sealed. Thereafter, the first and second substrates 2 and 3 are cut at predetermined portions thereof outside the first seal 4, thus obtaining a liquid crystal display panel.
And, in the method of manufacturing an LCD panel using the above described dispenser method, the opposite substrates are adhered to each other and brought into the reduced-pressure state in the vacuum container, and then the vacuum container is restored to the atmospheric pressure state. With such way, both substrates are pushed from the outsides thereof by a first reduced-pressure area 8 in the first seal 4 and a second reduced pressure area 9 formed between the first and second seals 4 and 5, and the seal material is squeezed, thus forming a desired gap.
However, when the balance of the pushing forces between the first and second reduced-pressure areas 8 and 9 is lost, a uniform gap cannot be formed from the center of the LCD panel to the periphery thereof.
Particularly, as in the method disclosed in the above described publication, in the method in which the liquid crystal material 6 is dropped onto the center of the display area, an interval between the first seal 4 and an area where the liquid crystal material 6 is dropped (hereinafter referred to as a dropped area) is large, and the first reduced-pressure area 8 is made too flat more than necessary as shown in FIG. 2. Accordingly, the gap becomes un-uniform, thus degrading display quality remarkably.
The present invention has been made in view of the above described problems, and a main object of the present invention is to provide a method of manufacturing the LCD panel capable of improving the display quality by making the gap between the substrates opposite to each other uniform.